1. Field of the Invention
The present invention relates to multilayer piezoelectric components each including a plurality of internal electrodes stacked between ceramic layers. Particularly, the present invention relates to a multilayer piezoelectric actuator and a method of manufacturing the same, an ink jet head using the piezoelectric actuator, a multilayer piezoelectric resonator used as a resonator, a band pass filter, or other electronic component, and a method of manufacturing the same, a piezoelectric transformer and a method of manufacturing the same.
The present invention also relates to a piezoelectric actuator having an electrode structure which is improved so as to significantly decrease variations in displacement and a manufacturing method therefor, an ink jet head, a multilayer piezoelectric resonator including a sintered compact body having an electrode structure which is improved to significantly widen a difference ΔF between the resonance frequency and antiresonance frequency, and to significantly decrease variations in resonance characteristics, and a manufacturing method therefor, a piezoelectric transformer having an electrode structure improved to significantly increase maximum efficiency and decrease variations in the maximum efficiency, and a manufacturing method therefor.
2. Description of the Related Art
An ink jet head of an ink jet printer uses a piezoelectric actuator for discharging a predetermined amount of ink. An example of conventional piezoelectric actuators will be described below with reference to FIG. 33.
A piezoelectric actuator 71 includes a sintered ceramic compact body 72. The sintered ceramic compact body 72 includes piezoelectric ceramic material such as lead titanate zirconate ceramic or the like.
In the sintered ceramic compact body 72, a plurality of internal electrodes 73a to 73l are arranged to overlap each other in the thickness direction. The internal electrodes 73a, 73c, 73e, 73g, 73i, and 73k are extended to the first side 72a of the sintered ceramic compact body 72. The other internal electrodes 73b, 73d, 73f, 73h, 73j, and 73l are extended to the second side 72b opposite to the first side 72a. 
First and second external electrodes 74 and 75 are disposed on the first side 72a and the second side 72b, respectively.
The ceramic layers disposed between the internal electrodes 73a to 73l are polarized in the thickness direction, as shown by arrows in FIG. 33. Namely, the ceramic layers on both sides of each of the internal electrodes are polarized in opposite directions of the thickness direction.
Therefore, application of a voltage between the external electrodes 74 and 75 causes displacement in a polarized portion of the piezoelectric actuator 71 due to a piezoelectric effect.
In an ink jet head of a conventional ink jet printer, displacement is caused in the piezoelectric actuator 71 to press an ink chamber so that a predetermined amount of ink is discharged from the ink chamber. Therefore, in order to discharge ink with high precision, it is required to decrease variations in displacement of the piezoelectric actuator 71.
However, the manufacture of many piezoelectric actuators 71 causes relatively large variations in displacement characteristics in the piezoelectric actuators. There is also the problem of causing variations in displacement in displacement portions when a plurality of notches are formed in the displacement portions of the piezoelectric actuator 71 in order to form a plurality of displacement portions.
Therefore, for example, an ink jet head of an ink jet printer including the above-described piezoelectric actuator is difficult to discharge a predetermined amount of ink with high precision.
FIG. 34 is a sectional view showing a conventional multilayer piezoelectric resonator.
A multilayer piezoelectric resonator 171 includes a sintered ceramic compact body 172 made of piezoelectric ceramic.
In the sintered ceramic compact body 172, a plurality of internal electrodes 173a to 173l are provided. The stacking direction of the internal electrodes 173a to 173l is located in the thickness direction. The sintered ceramic compact body 172 includes ceramic layers which are held between the internal electrodes in the thickness direction, and polarized as shown by arrows in FIG. 34. Namely, the adjacent ceramic layers are polarized in opposite directions in the thickness direction. The internal electrodes 173a to 173l are extended up to the opposite sides 712a and 172b of the sintered ceramic compact body 172.
Insulating films 174a to 174f and insulating films 175a to 175f are disposed on the sides 192a and 172b, respectively, of the sintered ceramic compact body 172. Each of the insulating films 174a to 174f and 175a to 175f is arranged to cover an exposed end of any one of the internal electrodes 173a to 173l on either of both sides 172a and 172b of the sintered ceramic compact body 172. Therefore, an end of each of the internal electrodes 173a to 173l is coated with any one of the insulating films 174a to 175f, the other end being exposed from the side 172a or 172b. 
External electrodes 176 and 177 are arranged to cover both sides 172a and 172b, respectively.
In the multilayer piezoelectric resonator 171, an alternating current electric field is applied between the external electrodes 176 and 177 to expand and contract the piezoelectric ceramic layers held between the respective internal electrodes 173a to 173l due to the piezoelectric effect, thereby obtaining resonance characteristics based on thickness longitudinal vibration.
However, in the piezoelectric resonator 171, resonance characteristics cannot be necessarily obtained according to design values, and a difference ΔF between the resonance frequency and antiresonance frequency tends to be lower than the desired value. A decrease in the frequency difference ΔF narrows the pass band of the filter.
Furthermore, the manufacture of many multilayer piezoelectric resonators 171 produces the problem of relatively large variations in resonance characteristics.
Also a Rosen-type piezoelectric transformer using a rectangular plate-shaped piezoelectric ceramic layer is conventionally known.
An example of conventional Rosen-type piezoelectric transformers will be described below with reference to FIGS. 35 and 36. A piezoelectric transformer 251 includes a rectangular plate-shaped sintered ceramic compact body 252 made of piezoelectric ceramic. The sintered ceramic compact body 252 is obtained by stacking green sheets with internal electrodes disposed therebetween, and then firing the resultant layered product, as shown in FIG. 36.
As shown in FIG. 36, green sheets 253 to 266 mainly composed of a piezoelectric ceramic powder are stacked in the direction shown in the drawing. First internal electrodes 267 are respectively disposed on the green sheets 253, 259, and 263 by screen printing conductive paste. Similarly, second internal electrodes 268 are respectively disposed on the green sheets 256, 262, and 266 by screen printing conductive paste.
Each of the first and second internal electrodes 267 and 268 contacts one end of a green sheet in the length direction. The first and second internal electrodes 267 and 268 are also arranged to overlap each other with ceramic layers held therebetween in the thickness direction. In the sintered ceramic compact body 252 (FIG. 35) as a final product, the internal electrodes 267 are exposed from the first side 252a along the longer side, and the second internal electrodes 268 are exposed from the second side 252b opposite to the first dies 252a. 
A first external electrode 269 is located in a portion of the first side 252a of the sintered ceramic compact body 252 in which the first internal electrodes 267 are exposed. Although not shown in the drawings, a second external electrode is also disposed on the second side 252b to be electrically connected to the second internal electrodes 268.
A direct-current voltage is applied between the first and second external electrodes to polarize the ceramic layers held between the respective first and second internal electrodes 267 and 268 in the thickness direction. In addition, a third external electrode 270 is disposed on a third side 252c along the short side of the sintered ceramic compact body 252.
Furthermore, a direct-current voltage is applied between the first external electrodes 269, the second external electrode and the third external electrode 270 to polarize the right-hand portion of the sintered ceramic compact body 252, where the internal electrodes 267 and 268 are not stacked, in the length direction of the sintered ceramic compact body, as shown by arrow P.
In the piezoelectric transformer 251, for example, the first external electrode 269 and the second external electrode function as input-side electrodes so that an input voltage is applied between the first and second external electrodes to excite the sintered ceramic compact body 252 in a length direction vibration mode, obtaining a stepped-up output voltage from the third external electrode 270 as an output electrode.
However, the piezoelectric transformer 251 cannot obtain maximum efficiency according to a desired value, and thus has a problem in that the maximum efficiency tends to be lower than the desired value. In addition, when the sintered ceramic compact body 252 is obtained by preparing a mother layered product for improving productivity, cutting the mother layered product into units of piezoelectric transformers 251 to obtain layered product chips, and then firing the layered product chips, or when the sintered ceramic compact body 252 is obtained by obtaining a mother sintered product, and then cutting the mother sintered product into sintered ceramic compact body s 252 of piezoelectric transformer units, there is the problem of relatively large variations in maximum efficiency of the piezoelectric transformers 251 as final products.